• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.6
• /
• pp.114-122
• /
• 2018

This study presents the emergency assessment method about seismic safety of cable-supported bridges using seismic acceleration sensors installed on the primary structural elements of them. The structural models of bridges are updated iteratively to make their dynamic characteristics to be similar to those of real bridges based on the comparison of their natural frequencies with those of real bridges estimated from acceleration data measured at ordinary times by the seismic acceleration sensor. The displacement at the location of each seismic acceleration sensor is derived by seismic analysis using design earthquake, and the peak value of them is determined as the disaster management criteria in advance. The displacement time history is calculated by the double integration of the acceleration time history which is recorded at each seismic acceleration sensor and filtered by high cut(low pass) and low cut(high pass) filters. Finally, the seismic safety is evaluated by the comparison of the peak value in calculated displacement time history with the disaster management criteria determined in advance. The applicability of proposed methodology is verified by performing the seismic safety assessment of 12 cable-supported bridges using the acceleration data recorded during Gyeongju earthquake.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.27 no.3
• /
• pp.137-145
• /
• 2014

We present a design sensitivity analysis(DSA) method for multiscale problems based on bridging scale decomposition. In this paper, we utilize a bridging scale method for the coupled system analysis. Since the analysis of full MD systems requires huge amount of computational costs, a coupled system of MD-level and continuum-level simulation is usually preferred. The information exchange between the MD and continuum levels is taken place at the MD-continuum boundary. In the bridging scale method, a generalized Langevin equation(GLE) is introduced for the reduced MD system and the GLE force using a time history kernel is applied at the boundary atoms in the MD system. Therefore, we can separately analyze the MD and continuum level simulations, which can accelerate the computing process. Once the simulation of coupled problems is successful, the need for the DSA is naturally arising for the optimization of macro-scale design, where the macro scale performance of the system is maximized considering the micro scale effects. The finite difference sensitivity is impractical for the gradient based optimization of large scale problems due to the restriction of computing costs but the analytical sensitivity for the coupled system is always accurate. In this study, we derive the analytical design sensitivity to verify the accuracy and applicability to the design optimization of the coupled system.

• Journal of Biosystems Engineering
• /
• v.37 no.3
• /
• pp.192-200
• /
• 2012

Purpose: Aerial application of chemicals with an agricultural helicopter allows for precise and timely spraying and reduces working labor and pollution. An attitude controller for an agricultural helicopter would be helpful to aerial application operator. The objectives of this paper are to determine the transfer function models and to estimate the handling qualities of a bare-airframe model helicopter. Methods: Transfer functions of a model unmanned helicopter were estimated by using NAVFIT and DERIVID modules of the $CIFER^{(R)}$ program to the time history data of frequency sweep flight tests. Control inputs of the transfer functions were elevator, aileron, rudder and collective pitch stick positions and the outputs were resulting on-axis movements of the fuselage. Results: Minimum realization of the transfer functions for pitch rate output to elevator control input and roll rate output to aileron control input produced second order transfer functions with undamped natural frequencies around 3.0 Hz and damping ratios of 0.139 and 0.530, respectively. The equivalent time delays of the transfer functions ranged from 0.16 to 0.44 second. Sensitivity analysis of the proposed parameters allowed derivation of minimal realization of the transfer functions. Conclusions: Handling quality of the model helicopter was addressed based on the eigenvalues of the transfer functions, corresponding undamped natural frequencies with damping ratios. The equivalent time delays of the lateral-directional motion ranged from 0.16 to 0.44 second, longer than the 0.1 to 0.15 second requirement for well-controlled typical manned aerial vehicles.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.14 no.3
• /
• pp.429-438
• /
• 1994

Three-dimensional analyses of multistory structures with wings using finite element models require tedious input data preparation, longer computation time. and larger computer memory. So this study lays emphasis on the development of efficient analysis models for a three-dimensional multistory structure with wings, including in-plane deformation of floor slabs. Since a three-dimensional multistory structure with wings is regarded as a combination of wing structures and their junction in this study, the proposed analysis models are easily applicable to multistory structures with plans in the shape of letters Y, U, H, etc. Dynamic analyses results obtained using proposed models are in excellent agreement to those acquired using three-dimensional finite element models in terms of natural vibration periods, mode shapes and displacement time history.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.38 no.5
• /
• pp.635-643
• /
• 2018

In the present study, influence of earthquake intensity range on seismic fragility analysis of a RC bridge has been evaluated. For this purpose, a RC bridge damaged by a past earthquake has been selected, and analytical model of the bridge has been developed for nonlinear dynamic time-history analysis. A total of 25 recorded earthquake motions have been employed for the nonlinear analysis from which maximum lateral drift ratio of piers are obtained. Then, seismic fragility analysis has been conducted for the bridge using the nonlinear analysis results. Probability of exceeding damage has been computed in terms of using the maximum likelihood estimation, and effect of earthquake intensity range of the motions on seismic fragility curves has been assessed analytically. Analytical predictions indicate that the earthquake intensity range is of utmost significance for rationale seismic fragility analysis reflecting a physical damage state of a bridge and seismic performance evaluation of such bridge.

• Earthquakes and Structures
• /
• v.8 no.5
• /
• pp.1127-1146
• /
• 2015

The excitation angle or angle of incidence is the angle in which the horizontal seismic components are applied with respect to the principal structural axes during a time history analysis. In this study, numerical simulations and parametric studies are performed for the investigation of the effect of the angle of seismic incidence on the response of adjacent buildings, which may experience structural pounding during strong earthquakes due to insufficient or no separation distance between them. A specially developed software application has been used that implements a simple and efficient methodology, according to which buildings are modelled in three dimensions and potential impacts are simulated using a novel impact model that takes into account the arbitrary location of impacts and the geometry at the point of impact. Two typical multi-storey buildings and a set of earthquake records have been used in the performed analyses. The results of the conducted parametric studies reveal that it is very important to consider the arbitrary direction of the ground motion with respect to the structural axes of the simulated buildings, especially during pounding, since, in many cases, the detrimental effects of pounding become more pronounced for an excitation angle different from the commonly examined 0 or 90 degrees.

• Wind and Structures
• /
• v.7 no.3
• /
• pp.145-158
• /
• 2004

The evaluation of the accumulation of permanent set for inelastic structures due to wind action is important in establishing a criterion to select a reduced design wind load and in incorporating the beneficial ductile behaviour in wind engineering. A parametric study of the accumulation of the permanent set as well as the ductility demand for bilinear single-degree-of-freedom (SDOF) systems is presented in the present study. The dynamic analysis of the inelastic SDOF system is carried out using the method of Newmark for artificially generated time history of wind speed. Simulation results indicate that the mean of the normalized damage rate is highly dependent on the natural frequency of vibration. This mean value is relatively insensitive to the damping ratio if the damping ratio is larger than 5%. The scatter associated with the accumulation of the permanent set is very significant. The consideration of the postyield stiffness can significantly reduce the accumulation of the permanent set if the ratio of the yield strength to the expected peak response is small. The results also show that the ductility demand due to the wind action over a period of one hour for flexible structures can be much less than that for rigid structures or structures with larger damping ratio if the SDOF systems are designed with a reduced peak response caused by the fluctuating wind.

• International Journal of Costume and Fashion
• /
• v.13 no.2
• /
• pp.65-77
• /
• 2013

The purposes of this study were to document the fashions adopted by young women in the United States in the 1980s and to explore if and how the dynamic shifts toward postmodernist values influenced those fashion trends. Fifteen U.S. women who were college students in the 1980s were interviewed for the study. In analysis of the data, we focused on social changes during the 1980s and the cultural impact of postmodernism vs. modernism as influential factors. Both postmodern and feminist ideas challenged the mainstream cultural framework of capitalism. U.S. women's styles and behaviors concerning dress reflected characteristics of postmodern consumption patterns, which include nostalgia, ethnic dress, androgyny, eclectic and novel clothing combinations, surprising or humorous appearance, and nonconformity. Despite the critique of conformity and conservatism in dress that had emerged in the 1960s and remained in at least minority or subversive trends, the importance of brand names and designer labels increased in mainstream fashion. This study helps us better understand the dynamics of fashion as it reflects societal and value changes in a transitional time in history.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.6 no.3
• /
• pp.87-93
• /
• 2002

A procedure for figuring out proper amount of additional viscous damping required to keep the inelastic deformation of a plan-wise asymmetric structure within a given target performance point was developed. To this end the behavior of an asymmetric nonlinear structure after yielding is investigated. Then a formula for the required amount of equivalent damping was derived based on the ductility demand of the structure. The procedure was applied to a five-story asymmetric structure subjected to an earthquake load. According to the comparison with the results from the dynamic time-history analysis, the structure with viscous dampers installed in accordance with the proposed procedure showed satisfactory seismic performance in both the stiff and the flexible edges.

• Advances in Computational Design
• /
• v.2 no.3
• /
• pp.211-223
• /
• 2017

This research presented a numerical and experimental study on the seismic performance of first-generation base-isolated and fixed-base nuclear power plants (NPP). Three types of the base isolation system were applied to rehabilitate the first-generation nuclear power plants: frictional pendulum (FP), high-damping rubber (HDR) and lead-rubber (LR) base isolation. Also, an Excel program was proposed for the design of the abovementioned base isolators in accordance with UBC 97 and the Japan Society of Base Isolation Regulation. The seismic assessment was performed using the pushover and nonlinear time history analysis methods in accordance with the FEMA 356 regulation. To validate the adequacy of the proposed design procedure, two small-scale NPPs were constructed at Universiti Teknologi Malaysia's structural laboratory and subjected to a pushover test for two different base conditions, fixed and HDR-isolated base. The results showed that base-isolated structures achieved adequate seismic performance compared with the fixed-base one, and all three isolators led to a significant reduction in the containment's tension, overturning moment and base shear.